1. Field of the Invention
The present invention relates to a liquid transporting apparatus which transports a liquid from a liquid supply port up to a plurality of liquid jetting ports, and an ink-jet printer.
2. Description of the Related Art
An ink-jet head which transports an ink supplied from an ink tank, and jets ink droplets from nozzles to a recording paper or the like has already been known. Ink-jetting methods are classified according to a difference in a method for generating jetting energy. There are ink-jetting methods such as a piezo method in which ink droplets are jetted by using a vibration force of a piezoelectric element, and a Bubble Jet® method in which ink droplets are jetted by generation of air bubbles by heat energy. Among these, the piezo method has advantages (merits) such as a high degree of freedom of selecting types of ink, a possibility of a liquid droplet gradation by controlling precisely jetting amount of the ink, and a high durability, since a mechanical power is used as the jetting energy.
For example, An ink-jet head of the piezo method disclosed in Japanese Patent Application Laid-open No. 2006-44242, includes a channel unit which is provided with a plurality of pressure chambers, in channels from an ink supply port up to a plurality of nozzles, corresponding to each of the nozzles, and a piezoelectric actuator which is stacked on the channel unit, and which selectively changes a volume of each of the pressure chambers. Moreover, the piezoelectric actuator has a vibration plate which serves as a common electrode, a piezoelectric layer which is formed on an upper surface of the vibration plate, and a plurality of individual electrodes which are formed on an upper surface of the piezoelectric layer, corresponding to the pressure chambers respectively.
According to such ink-jet head, when a drive voltage is selectively applied to one of the individual electrodes of the piezoelectric actuator, an electric field acts in a portion (active portion) of the piezoelectric layer sandwiched between the individual electrode and the common electrode, and there occurs a deformation in a direction of thickness of the piezoelectric layer. Moreover, this deformation of the piezoelectric layer is propagated to the vibration plate, and a volume of a pressure chamber corresponding to the individual electrode is changed. Due to a pressure fluctuation generated in an ink inside the pressure chamber, ink droplets are jetted from a nozzle corresponding to the pressure chamber.
However, when an environmental temperature is low, since a viscosity of an ink in the ink-jet head becomes high, if it is intended to jet from the nozzles, ink droplets similar as ink droplets at a high temperature, it is necessary to increase the pressure fluctuation inside the pressure chamber by increasing the drive voltage of the piezoelectric actuator. When the drive voltage of the piezoelectric actuator is increased, electrical components which can withstand high voltage are to be used as electrical components which are connected to the ink-jet head, and this leads to an increase in an overall cost.
In Japanese Patent Application Laid-open No. 2000-198192, an ink-jet head, in which a heater made of a high-resistance material is provided to a part of a common electrode on a lower portion of the piezoelectric actuator, has been disclosed. In this ink-jet head, piezoelectric vibrator and an individual electrode (upper electrode) are stacked on the heater, with an object of preventing malfunctioning of the piezoelectric vibrator due to dew formation (dew condensation). In a case of this ink-jet head, the heater is formed on a part of the common electrode, and it is necessary to apply an electric current to the common electrode for making the heater generate heat. Therefore, it is not possible to make the heater generate heat simultaneously with driving of the piezoelectric actuator for which it is necessary to keep an electric potential of the common electrode zero.